Equipment:The subject top reactor inlet flanged elbows are part of the reactors pressure boundary and designed under ASME Section VIII Div. 2 provisions, thus shall be ASME U2 stamped. 2¼ Cr 1 Mo steel forgings  shall conform to the latest ASME Code Sec II Part A and Part D 2015 edition for the following material specifications : Flanges: SA 336 F22 CL 3

Problem:Findings pertaining to 18â€� Removable Top Spool Weld Overlay and repair progression. Following highlights the major points. Presence of new indications on the 30in€� flange face. These indications look like two concentric circles with common center.  The indications are extended circumferentially 3.5 inch distance (maximum) from the flange bore. The ring groove was 100% PT inspected prior to the bake out process. The indications morphology and lack of crack presence in the hydrocracker flange face indicate that these cracks were most probably pre-existing and associated to the manufacturing process, rather than operating conditions. The temperature report for subject hydrocracker did not show any abnormality and recorded operating temperature at the inlet nozzle for C-100 did not exceed 850F. The flange face weld overlay thickness was found to be 4.5mm thick. Shear Weave UT was performed and indicated that the depth of the crack is 3mm maximum, leaving 1.5mm weld overlay deposit ligament thickness underneath the crack. These cracks are not in the pressure retaining boundary and will not experience significant hoop stresses. Therefore, the indications can be left without repair. In addition, these cracks are in the portion of the flange that is redundant in terms of the thickness given that the matching flange bore is 762mm.

Analysis: A detailed stress-analysis using FEA for the 30" Flange (R-102) of the 30in€� x 18in Elbow Spool currently undergoing repair, and following are the highlights. The following loads were considered. Maximum operating pressure of 2,545psi @ 850F. Design Bolt Tightening Loads based on 18,000psi bolt stress value. Hydrostatic end force of 518,232 lbs acting on the area inside the flange. Hydrostatic end force of 3,110,248 lbs acting on the nozzle neck. Appropriate BCs were applied based on the 90deg sector solid model.

Benefits: Timely completion of T&I activities without compromising mechanical integrity.

Results Conclusion:From the von-mises stress solution it is evident that overall all the stresses in the flange are well under the allowable stresses. The flange bottom half in in tension, as expected, due to the applied bolt loads and the restraining RTJ gasket seat. Also, the stress analysis confirms that as these cracks are not in the pressure retaining boundary, they are experiencing negligible hoop stresses.  The upper half of the flange, especially the flange face from the bore extending out to the groove, experiences the least magnitude of 3ksi stress, again as expected and thus confirms that these cracks are in the portion of the flange that is redundant in terms of the thickness given that the matching flange bore is 762mm. Therefore, the indications could be left without repair.